1. Field of the Invention
The present invention relates to a coupling construction and more particularly to the coupling construction preferable for connecting a high voltage terminal of an ignition coil for use in an internal combustion engine and an electric conductor with each other.
2. Description of the Related Arts
An example of the internal combustion engine disclosed in Japanese Laid-Open Utility Model Publication No. 64-8580 is described below with reference to FIG. 4. An electric conductor 5 is engaged by the inner peripheral surface of an insulating member 4 with the insulating member 4 installed on an installing hole 3 formed in a cylinder head 2. A terminal 6 mounted above the electric conductor 5 is urged by a spring 7 so as to bring the terminal 6 into contact with a high-voltage terminal 9 of an ignition coil 8 inserted into an upper portion of the insulating member 4. At the same time, a terminal 10 provided at a lower portion of the electric conductor 5 is urged by a spring 11 so as to bring the terminal 10 into contact with a terminal 13 of an ignition plug 12 inserted into a lower portion of the insulating member 4.
In the above-described ignition device, it is necessary to increase electrical sealing performance between the insulating member 4 and the ignition plug 12 with the rise of a required voltage. To this end, the inner diameter of the insulating member 4 is set to be small for the insulating member 4 to tighten an insulating portion 12a of the ignition plug 12 strongly.
In the construction of the above-described ignition device, the ignition coil 8 and the electric conductor 5 can be uncoupled from each other. Therefore, when the ignition coil 8 is moved upward by hand in removing the ignition device from an engine 1, the ignition coil 8 is uncoupled from the insulating member 4 before the insulating member 4 is uncoupled from the ignition plug 12. This is because the ignition plug 12 is strongly tightened by the insulating member 4. As a result, the insulating member 4 or the electric conductor 5 remains disposed in the installing hole 3 of the engine 1.
It is conceivable that the ignition coil 8 is tightened by the insulating member 4 to a greater extent. But the force of inserting the ignition coil 8 is increased and thus the operation of inserting the ignition coil 8 into the insulating member 4 is inefficiently performed. It is also conceivable that the ignition coil 8 is adhered to the insulating member 4. But it is impossible to replace other parts.